1. Field of the Invention
The present invention relates to an electrical overload protection device that is integrated directly on the underlying structure of an electronic device. More particularly, the device which functions as a thermal fuse, is integrated directly on the substrate of a semiconductor device, and serves to protect associated system elements from electrical overstress conditions, thus insuring a failsafe mode of operation.
2. Description of Prior Art
A variety of fuses and breaker switches exist to protect electrical circuits or devices from overstress conditions. Such overstress conditions might include, for example, a lightning strike, a power surge, or more simply an overload condition being supplied at the power input terminal of the circuit or device. When such an overload condition exists, the electrical resistance of the device produces heat. While heat dissipation devices can be used (e.g., fans, heatsinks, and the like), they are generally not adequate to compensate for extreme overload conditions. If the overload condition persists, then the heat buildup may become great enough to melt and/or destroy key components, or the entire electrical circuit. Fires might even result in one component or device, and the fire can then spread and destroy an entire system.
In the past, thermal fuses have been used to guard against overstress conditions. A thermal fuse uses the heat generated by the electrical resistance and overload condition to break the electrical connection between two points on the circuit. This is usually accomplished by the overload condition heat causing an electrical contact point to melt, thereby severing the contact. In the past, such thermal fuses have been incorporated, as separate devices between the power input and an electrical device to be protected.
Several drawbacks exist, however, to the use of separate and distinct thermal fusing components. By way of example, and not limited to such, these drawbacks might include; first, thermal fuses are generally large components, and may be hard to incorporate in smaller electrical packages, particularly semiconductor packages; second, the thermal fuse might, under certain conditions, explode or expel byproducts, thereby damaging neighboring components or devices which the fuse was ultimately slated to protect; and third, the contact point material, which melts during an overstress condition, might drip or flow over neighboring components. Such hot, dripping material might thereafter cause short circuits, further overheating, fires, and/or other related damage to the neighboring components. Ultimately the entire system into which the components were incorporated might fail or be damaged. Moreover, separate thermal fuse components are generally not an integral part of the circuit which is generating heat due to the overstress condition. As a result, it is difficult for the fuse and the circuit to be at the same temperature. It is therefore possible that the device may overheat sufficiently before the separate fuse component opens, thereby causing a possible hazardous failure condition. One such condition would be where the device connections meet (or short out) and the resulting failure causes the device to fall off the printed circuit board to which it was soldered. This wayward part could thereby result in a possible short circuit or fire hazard in surrounding boards, or system-wide.
Accordingly, what is needed in the field is a thermal fuse which exists, or can be formed, integrally with an overall circuit, or collection of components. In particular, the thermal fuse should be capable of achieving a very small size, and yet still provide adequate overstress condition protection. The fuse should be integrated in the foundational material of the underlying device. Incorporation into a semiconductor circuit substrate would prove to be most useful. The fuse should also operate without jeopardizing neighboring components with dripping contact material, expulsions, or the like.